Membrane-associated immunoglobulin (M-Ig) was isolated from Daudi cells which had been radioiodinated using lactoperoxidase. This M-Ig was found to have a molecular size on SDS-PAGE of 330,000 daltons. The component protein chains (µ and K) have molecular sizes of 75,000 and 33,000 daltons, respectively. Further studies showed that [3H]galactose can be incorporated into K-chains, but that extra protein and not carbohydrate was responsible for the increased molecular size of this molecule.

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